JP4254626B2 - Injection device for injection molding machine and foam injection molding method - Google Patents

Description

  The present invention relates to an injection apparatus and a foam injection molding method of an injection molding machine, and in particular, injection of an injection molding machine suitable for obtaining a foamed product of resin by injecting and filling resin into a mold. The present invention relates to an apparatus and a foam injection molding method.

  As a foam injection molding method to obtain foam molded products, short shot method in which molten resin mixed with foaming agent is injected and filled in the mold in a short shot state, and then the resin is foamed in the mold, and foaming agent is mixed A full shot method in which the molten resin thus obtained is injected and filled in a mold in a full shot state, and then the resin is foamed while the mold is opened is generally known.

FIG. 4 shows an example of an injection apparatus of an injection molding machine that can be applied to any conventional foam injection molding method.
The injection apparatus shown in FIG. 4 includes a heating cylinder 32, an injection molding screw 31 that is housed in the heating cylinder 32 and has a spiral flight, and a hopper 34 that supplies a resin mixed with a foaming agent into the heating cylinder 32. The injection molding screw 31 moves the injection molding screw 31 in the heating cylinder 32 so as to advance and retreat in the axial direction, and the hydraulic motor 36 rotates the injection molding screw 31 in the heating cylinder 32. A hydraulic source 37 for supplying desired pressure oil to the cylinder 35 and the hydraulic motor 36 and a control device 38 are provided, and a heater (not shown) is attached to the outer peripheral surface of the heating cylinder 32.

  The injection device is configured such that the resin mixed with the foaming agent is supplied from the hopper 34 into the heating cylinder 32 when the injection molding screw 31 is rotated by the hydraulic motor 36, and the supplied foaming agent is provided. The resin mixed with is heated by a heater (not shown) attached to the heating cylinder 32, and is sent to the front of the injection molding screw 31 while being melted by the kneading compression action by the rotation of the injection molding screw 31. The molten resin sent to the front of the injection molding screw 31 is injected and filled into a mold cavity (not shown) from the nozzle 33 attached to the tip of the heating cylinder 32 by the injection molding screw 31 advanced by the injection cylinder 35. A foam injection molded product can be obtained. (See Patent Document 1)

For the injection molding screw 31 of the injection device, a high dispersion type generally known from the past is used. FIG. 5 shows an example of a screw tip structure for a high dispersion type conventional injection molding screw.
The injection molding screw 31 shown in FIG. 5 is formed on the screw main body 42 provided with a spiral flight 45 for delivering resin, the screw head 43 fixed to the tip of the screw main body 42, and the screw head 43. And a mixing head 44 in which a plurality of protrusions 46 are formed in the circumferential direction of the outer peripheral surface and in a plurality of rows in the axial direction.

  Then, the molten resin fed from the screw main body 42 shown in FIG. 5 passes through the mixing head 44, meanders while branching or joining the gaps between the protrusions 46, and is well dispersed. (See Patent Document 2)

Japanese Patent Application No. 2002-52591 Japanese Patent Laid-Open No. 8-1556047

However, when performing foam injection molding with a chemical foaming agent using the above-described conventional injection device, the chemical foaming agent aggregates in the protrusions of the mixing head, and coarse foam cells are mixed, resulting in a non-uniform foaming state. There was a problem.
In addition, the injection device provided with the conventional injection molding screw has a problem that the color change is poor because the molten resin tends to stay in the protrusions of the mixing head.

  Furthermore, the conventional injection device described above has a structure in which the check ring and the mixing head are in direct contact with each other to prevent the flow of the resin, so that the sealing surface is damaged by foreign matters in the molten resin and the performance of preventing the back flow is lowered. Then, there was a problem that the expensive mixing head had to be replaced.

  Further, in recent years, resin moldability has been improved, and a high flow resin (high flow material) having a melt flow rate (melting index, ISO-1133) of 20 g / 10 min or more is often used for injection molding. It was. However, when the above-described conventional injection apparatus is used to mix and foam the injection molding with the above-described high-fluidity resin, the chemical foaming agent is contained in the molten resin having a low-viscosity high-fluidity resin. Difficult to disperse, resulting in poor dispersion of the foaming agent in the molten resin, causing the problem of poor foaming.

  The present invention pays attention to the above-mentioned problems of the prior art, and even in the case of foam injection molding, the resin can be uniformly dispersed, the chemical foaming agent is excellent in kneading and dispersibility, and a fine and uniform foam cell assembly. It is an object of the present invention to provide an injection apparatus for an injection molding machine and a foam injection molding method for obtaining a foamed molded article.

In order to achieve the above object, an injection apparatus according to the present invention comprises:
(1) Screw body inserted in a heating cylinder so as to be rotatable in the circumferential direction and removably in the axial direction, a mixing head detachably fixed to the tip of the screw body, and a reverse flow to the tip of the mixing head A plurality of screw heads having a prevention device and detachably fixed to the mixing head, wherein a plurality of annular grooves adjacent to the plurality of rows of annular grooves communicate with the outer peripheral surface of the mixing head. An axial groove is formed, and the injection molding screw is formed so that the resin passage area in the cross section perpendicular to the axial direction of the axial groove decreases from the screw body side toward the screw head side.
The injection molding screw is moved backward by feeding the resin mixed with the foaming agent supplied from the hopper to the front of the screw head while rotating and mixing and melting the injection molding screw. The molten resin containing the foaming agent that was advanced and fed forward of the screw head was injected and filled into the mold cavity.

(2) In the injection device according to (1), the plurality of axial grooves communicating with the annular groove are provided with an equal number of divisions in the circumferential direction of the outer peripheral surface of the mixing head. By forming the groove pitch so that the center position of each groove adjacent in the direction is the center position of each other, the groove pitch is shifted to one half of the circumferential direction (each), thereby forming a mesh on the outer surface of the screw head. Shaped grooves were formed.

(3) In the injection device according to (1) or (2), the number of grooves in the axial direction is a mesh on the outer peripheral surface of the screw head, with the number of equal divisions in the circumferential direction of the outer peripheral surface of the mixing head being 15 or more. Shaped grooves were formed.

In order to achieve the above object, the foam injection molding method according to the present invention comprises:
(4) Screw body inserted in the heating cylinder so as to be rotatable in the circumferential direction and capable of moving back and forth in the axial direction, a mixing head fixed to the tip of the screw body so as to be detachable, and a reverse flow to the tip of the mixing head A plurality of screw heads having a prevention device and detachably fixed to the mixing head, wherein a plurality of annular grooves adjacent to the plurality of rows of annular grooves communicate with the outer peripheral surface of the mixing head. An axial groove is formed, and an injection molding screw formed so that the passage area of the resin in the cross section perpendicular to the axial direction of the axial groove decreases from the screw body side to the screw head side,
The resin mixed with the foaming agent supplied from the hopper is moved forward by screwing the injection molding screw to the front of the screw head while mixing and melting the screw body, and then the injection molding screw is moved forward. The molten resin containing the foaming agent fed to the front of the screw head was injected and filled into the mold cavity.

  (5) In the foam injection molding method described in (4), a high flow resin (high flow material) having a melt flow rate (melting index, ISO-1133) of 20 g / 10 min or more when a resin mixed with a foaming agent is melted ).

  According to the injection device of the injection molding machine of the present invention, a mesh-like groove portion that repeats branching and joining from the screw body side toward the screw head side is formed on the outer peripheral surface of the mixing head, and the mesh-like shape is formed. Since the resin passage area when the axial groove of the groove is cut in the direction perpendicular to the axis is reduced from the screw body side to the screw head side, the resin can be homogenized and the foaming agent can be kneaded. Excellent dispersibility. Therefore, the foaming agent is uniformly dispersed in the molten resin, and a molded product of a fine and uniform foamed cell aggregate without coarse foamed cells can be obtained.

  And, forming a plurality of rows of annular grooves on the outer peripheral surface of the mixing head, forming grooves extending in the axial direction through the adjacent annular grooves, and forming a plurality of rows in the circumferential direction and a plurality of rows in the axial direction, In each row of grooves formed in a plurality of rows in the axial direction, a mesh is formed so that the rows formed in the circumferential direction are the same, and the rows adjacent in the axial direction are shifted to each other by a half pitch (each). Since the groove is formed, the resin sent to the mixing head repeats branching and merging, and the foaming agent is well dispersed. Further, the mesh-like groove portion of the mixing head has few stagnant portions and is excellent in color changeability without a sudden change in cross-sectional area.

  According to the foam injection molding method of the present invention, a mesh-like groove portion that repeats branching and merging from the screw body side toward the screw head side is formed on the outer peripheral surface of the mixing head, and the groove portion formed in the mesh shape. Since the resin passage area when cutting the axial groove in the direction perpendicular to the axis decreases from the screw body side toward the screw head side, the resin can be homogenized and the foaming agent can be kneaded and dispersed. Excellent in properties. Therefore, there is an excellent effect that the chemical foaming agent aggregates in the mixing head and coarse foamed cells are mixed so that the foamed state is not uniform.

  Further, in the mesh-like grooves formed on the outer peripheral surface of the mixing head, the number of grooves extending in the axial direction is equal to or more than 15 in the circumferential direction, so that the melt flow rate (melting index, ISO− Even if 1133) is a high fluidity resin of 20 g / 10 min or more, since the foaming agent is uniformly dispersed as a whole, it has an excellent effect of preventing foaming failure.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
1 and 2 relate to an embodiment according to the present invention, FIG. 1 is a sectional view of an injection apparatus showing a preferred example of an embodiment according to the present invention, and FIG. 2 illustrates an embodiment of a mesh groove on the outer peripheral surface of a mixing head. FIG.
Here, in FIG. 2, in each row of the annular grooves formed in a plurality of rows in the axial direction on the outer peripheral surface of the mixing head, the number of divisions equally divided in the circumferential direction is the same, and the rows adjacent in the axial direction are set at a pitch of 2. A case is shown in which a mesh is formed so that a plurality of rectangular partitions are formed by shifting to a half.

The structure of the injection apparatus 50 of the injection molding machine which is embodiment of this invention is demonstrated.
In FIGS. 1 and 2, reference numeral 41 denotes an injection molding screw built in the heating cylinder 23, and includes a screw body 11, a mixing head 12, a screw head 13, and a backflow prevention device 40. The backflow prevention device 40 includes a check ring 14 and a seat 15.
The injection device 50 includes a hopper that supplies a resin mixed with a foaming agent into the heating cylinder 23, an injection cylinder that moves the injection molding screw 41 in the heating cylinder 23 so as to be movable forward and backward, and the injection cylinder. A hydraulic motor that rotates the molding screw 41 in the heating cylinder 23, a hydraulic source that supplies desired pressure oil to the injection cylinder and the hydraulic motor, and a control device; Is installed.

The mixing head 12 includes a screw portion 16 that is screwed into an opening at the tip of the screw main body 11, and is detachably attached to the screw main body 11. The screw head 13 includes a screw portion 17 that is screwed into the opening at the tip of the mixing head 12, and is detachably attached to the mixing head 12.
The mixing head 12 is formed of a large-diameter portion on the screw head 13 side and a small-diameter portion formed with a screw portion 16 that is screwed into the opening at the tip of the screw main body 11 on the screw main body 11 side. A plurality of holes 21 for the mixing head 12 detaching tool are provided on the end face on the screw head 13 side.
In addition, the maximum outer diameter of the large diameter portion of the mixing head 12 is smaller than the inner diameter of the heating cylinder 23 and larger than the valley diameter of the screw body 11. Further, in the large-diameter portion of the mixing head 12, the valley diameter formed at the end portion on the screw body 11 side is matched with the valley diameter of the adjacent screw body 11, and the valley diameter on the screw head 13 side end surface is the outer diameter of the sheet 15. Therefore, the molten resin does not stay and the step at the joint is eliminated.

Here, as shown in FIG. 1, a plurality of annular grooves 20 are formed on the outer peripheral surface of the mixing head 12, and the axial grooves extending in the axial direction are connected to the adjacent annular grooves 20. 18 is formed in a plurality of rows in the circumferential direction and in a plurality of rows in the axial direction, and in each row of the axial grooves formed in the plurality of rows in the axial direction, the number of divisions equally divided in the circumferential direction is the same. By forming the columns adjacent in the axial direction so as to be shifted from each other by a half of the pitch, a mesh-like groove portion is formed so as to form a rectangular partition wall shown in a developed view in FIG.
In order to reduce the passage area of the resin when the axial groove 18 is cut in the direction perpendicular to the axial direction in the groove portion, the screw body 11 The outer diameter on the sheet 15 side is larger than the valley diameter.

Further, in the injection apparatus 50 of the injection molding machine shown in FIG. 1, the valley diameter dimension of the annular groove 20 communicating with the valley diameter dimension of the axial groove 18 is increased toward the screw head side. The width of the groove was adjusted so that a sudden pressure change or the like does not occur when the resin flows from the axial groove 18 into the annular groove 20.
Here, the ratio of the resin passage area between the screw body 11 side and the screw head 13 side in the present invention is preferably in the range of 1: 0.9 to 0.3, and the melt flow rate of the resin to be molded and the foaming agent It is appropriately selected depending on the type, amount, expansion ratio and the like.

It is needless to say that the shape of the groove is not limited to the shape shown in FIG. 2, and it is only necessary to repeat the branching and merging from the screw body 11 side to the screw head 13 side.
Further, the method of reducing the resin passage area when the axial groove 18 is cut in the direction perpendicular to the axis is not limited to the above method, and the valley diameter of the groove portion of the mixing head 12 is the same dimension, and the circular groove of the axial groove 18 is used. A method of decreasing the circumferential width from the screw body 11 side toward the screw head 13 side may be used.

The screw head 13 is adjacent to a small diameter portion for attaching a backflow prevention device 40 to be described later at a head portion formed in a substantially conical shape, and a screw portion 17 that is screwed into the opening portion of the mixing head 12 at the small diameter portion. It is the structure which formed.
Then, the check ring 14 is gently fitted from the small diameter portion of the screw head 13, and the screw portion 17 of the screw head 13 is screwed into the tip opening portion of the mixing head 12, whereby the sheet is mixed between the mixing head 12 and the screw head 13. 15 is sandwiched. As a result, the backflow prevention device 40 including the check ring 14 and the seat 15 is detachably attached between the mixing head 12 and the screw head 13.
The check ring 14 is axially movable back and forth outside the small diameter portion at the tip of the screw head 13, and comes into contact with the sheet 15 when moved toward the screw body 11 by the pressure of the molten resin during injection filling. The molten resin at the tip is prevented from flowing back to the screw body 11 side.
Further, in the measuring process in which the screw main body 11 moves backward while rotating, the check ring 14 moves toward the screw head 13. The molten resin sent from the screw main body 11 passes through the gap between the check ring 14 and the sheet 15, which is a passage portion of the backflow prevention mechanism 40, and the gap between the check ring 14 and the screw head 13. Is sent to.

  Further, since the injection molding apparatus 50 according to the present embodiment shown in FIG. 1 fixes the screw body 11, the mixing head 12, the backflow prevention device 40, and the screw head 12 so as to be detachable, for example, the backflow prevention device of FIG. Even if the sealing surface is damaged by foreign matter in the molten resin and the performance of preventing the backflow is reduced, the backflow prevention device 40 can be removed from the mixing head 12 and replaced with another backflow prevention device. It has an excellent effect that there is no need to replace the.

  Furthermore, if the type of resin material or foaming agent to be handled and the injection molding screw are not compatible, the mixing head can be removed from the screw body and replaced with another compatible mixing head, and the expensive screw body must be replaced. There is no.

Next, a foam injection molding method using the injection apparatus 50 of the injection molding machine configured as described above will be described.
The resin material applicable to the present invention is obtained by mixing a chemical foaming agent with a thermoplastic resin typified by polystyrene or polypropylene that can be injection-molded. As the chemical foaming agent, an inorganic foaming agent represented by sodium bicarbonate or an organic foaming agent represented by azodicarbonamide is used.

Resin mixed with a chemical foaming agent supplied from a hopper (not shown) receives the heat energy of the heater attached to the outer peripheral surface of the heating cylinder 23 in the heating cylinder 23, and supplies, compresses, and measures the screw body 11. And is plasticized and melted by the mechanical energy accompanying the rotation of the screw body 11 and sent to the mixing head 12. And it flows into the mesh-like groove part formed in the outer peripheral surface of the mixing head 12 and repeats branching and merging by the rotation of the axial groove 18, annular groove 20, partition wall 19 and injection molding screw 41, and the foaming agent Are dispersed without agglomeration.
The molten resin sent to the mixing head 12 is sent to the front of the screw head 13 through the passage portion of the backflow prevention device 40, and the injection molding screw 41 is moved backward by the pressure. The molten resin fed to the front of the screw head 13 is injected by the advancement of the injection molding screw 41 and is filled into the mold cavity from the nozzle 24 attached to the tip of the heating cylinder 23.

Hereinafter, the characteristic operation and effects of the injection apparatus 50 according to the present invention will be described in detail.
In the present invention, a mesh-like groove portion that repeats branching and merging from the screw body 11 side to the screw head 13 side is formed on the outer peripheral surface of the mixing head 12, and the grooves in the axial direction of the mesh-like groove portions are formed. The resin passage area when cut in the direction perpendicular to the axis is configured to decrease from the screw body 11 side toward the screw head 13 side.
As described above, a general high dispersion screw uses a protrusion formed on a mixing head as a partition wall to branch or join the resin, thereby kneading the resin and dispersing the foaming agent. However, there is a limit to its function and effect. For example, when a powdery foaming agent is dispersed in the resin, a portion where the resin tends to stay in the groove portion of the mixing head is generated. When the foaming agent contained is aggregated in the staying part, a problem such as foaming failure is likely to occur, and this problem is particularly likely to occur in a part where a sudden change in the pressure and speed of the molten resin occurs.
In order to prevent this, it is necessary to uniformly knead the resin as a whole, and means such as increasing the number of branching and merging of the resin more than before or passing through a narrow resin passage are effective.
For example, as a method of increasing the number of branching and merging of the resin as compared with the conventional method, if the number of divisions of the grooves extending in the axial direction is equally divided into 15 or more in the circumferential direction, the dispersion effect of the foaming agent is greatly improved. .

For the reasons described above, according to the injection apparatus 50 of FIG. 1 according to the present invention, a narrow resin passage (a groove having a small cross-sectional area) is generated without causing a sudden change in the pressure or speed of the molten resin flowing in the mixing head 12. The molten resin repeats static branching and merging, and the foaming agent dispersed in the molten resin does not cause aggregation.
Using the injection apparatus and foam molding method of the injection molding machine according to the present invention, an azo-based chemical foaming agent is mixed with polypropylene resin and injection molding is performed to obtain a foam molded article having a fine and uniform foam cell assembly. I was able to.

  In addition, a plurality of axial grooves 18 that extend in the axial direction and communicate with the plurality of rows of annular grooves 20 on the outer peripheral surface of the mixing head 12 are formed in a plurality of rows in the circumferential direction and in the axial direction. In each row of grooves forming the row, the number of equally divided portions in the circumferential direction is the same, and the rows adjacent to each other in the axial direction are offset from each other by half with respect to each other in pitch. No. 50 has an excellent advantage that it is easy to manufacture and easy to perform maintenance such as cleaning after use.

In the present embodiment, the drive mechanism is a hydraulic injection device. However, the present invention is not limited to this embodiment applicable to the present invention, and the drive mechanism injection device using an electric servo is used in the present invention. May be.
The injection device and the foam injection molding method of the present invention include a short shot method in which a molten resin mixed with a foaming agent is injected and filled into a mold in a short shot state, and then the resin is foamed in the mold. The present invention can be applied to any foam injection molding method of the full shot method in which a molten resin mixed with an agent is injected and filled in a mold in a full shot state, and then the resin is foamed while opening the mold.

  Further, since the injection device and the foam injection molding method of the present invention are excellent in dispersibility, a molded product of a uniform and fine foam cell assembly can be obtained with a small amount of foaming agent. The mold air vent is reduced in clogging and has an excellent effect of preventing the strength of the molded product from being lowered due to residual unreacted foaming agent.

The mixing head used in the injection apparatus and the foam injection molding method of the injection molding machine of the present invention shown in FIG. 1 has an opening at the tip of the screw body 11 and an opening at the small diameter portion of the screw head 13a as shown in FIG. The structure provided with the screw parts 16 and 22 screwed together may be sufficient.
And even if the mixing head which is embodiment of this invention is used for the extrusion apparatus of resin, and foaming extrusion of resin, the effect similar to the above can be exhibited.

It is sectional drawing which shows a preferable example of the screw front-end | tip structure in the injection device as embodiment by this invention. It is an expanded view for demonstrating embodiment of the mixing head outer peripheral surface mesh-like groove part by this invention. It is sectional drawing for demonstrating the screw front-end | tip structure in the injection device as other embodiment by this invention. It is sectional drawing for demonstrating an example of the injection apparatus of the conventional injection molding machine. It is sectional drawing for demonstrating an example of the screw tip structure of the conventional screw for injection molding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Screw main body 12 Mixing head 13 Screw head 18 Axial groove 19 Partition 20 Ring 20 Groove 23 Heating cylinder 40 Backflow prevention device 41 Injection molding screw 50 Injection device

Claims (5)

A screw body inserted in a heating cylinder so as to be rotatable in the circumferential direction and removably in the axial direction, a mixing head fixed detachably to the tip of the screw body, and a backflow prevention device at the tip of the mixing head A screw head that is detachably fixed to the mixing head,
A plurality of axial grooves are formed on the outer peripheral surface of the mixing head to connect the annular grooves adjacent to the plurality of rows of annular grooves, and the resin passes through the cross section perpendicular to the axial direction of the axial grooves. With an injection molding screw formed so that the area decreases from the screw body side toward the screw head side,
The injection molding screw is moved backward by feeding the resin mixed with the foaming agent supplied from the hopper to the front of the screw head while rotating and mixing and melting the injection molding screw. An injection apparatus of an injection molding machine that injects and fills a molten resin containing a foaming agent that has been advanced and fed forward of the screw head into a mold cavity. The plurality of axial grooves communicating with the annular groove are equally divided in the circumferential direction of the outer peripheral surface of the mixing head, and the same number of divisions are provided. 2. The injection apparatus for an injection molding machine according to claim 1, wherein the groove pitch is formed so as to be shifted to one half (each) in the circumferential direction so as to be the center position of the groove pitch . The injection device of the injection molding machine according to claim 1 or 2, wherein the number of grooves in the axial direction is equal to or greater than 15 in the circumferential direction of the mixing head outer circumferential surface . A screw body inserted in a heating cylinder so as to be rotatable in the circumferential direction and removably in the axial direction, a mixing head fixed detachably to the tip of the screw body, and a backflow prevention device at the tip of the mixing head A screw head that is detachably fixed to the mixing head,
A plurality of axial grooves are formed on the outer peripheral surface of the mixing head to connect the annular grooves adjacent to the plurality of rows of annular grooves, and the resin passes through the cross section perpendicular to the axial direction of the axial grooves. Using an injection molding screw formed so that the area decreases from the screw body side toward the screw head side,
The injection molding screw is moved backward by feeding the resin mixed with the foaming agent supplied from the hopper to the front of the screw head while rotating and mixing and melting the injection molding screw. A resin foam injection molding method in which a molten resin containing a foaming agent that has been advanced and fed forward is injected and filled into a mold cavity.   The foam injection molding method according to claim 4, wherein a melt flow rate (melting index, ISO-1133) when the resin mixed with the foaming agent is melted is a high fluidity resin (high flow material) of 20 g / 10 min or more. .

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